Method and device for forming conical tube casings

ABSTRACT

To form metal sheet blanks into taper tubes, a die is provided which has a conical cavity into which a conical punch plunges. The punch is led into the die along a curve. Taper tube shells can easily be fabricated by this method.

CROSS REFERENCE TO RELATED APPLICATION

Applicant hereby claims foreign priority benefits under 35 U.S.C. § 119of PCT Application No. CH00/00202, filed Apr. 6, 2000, the disclosure ofwhich is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method and apparatus for forming metal sheetsinto taper tube shells.

Taper tubes are desired for a multitude of applications. However, tapertube shells that can subsequently be welded to make a taper tube areexpensive to fabricate.

Therefore the fundamental problem of the invention is to offer a simpleway of rounding sheets conically.

SUMMARY OF THE INVENTION

This problem is solved in the case of a method of the kind stated at theoutset, by employing a conical die and punch to deform an individualsheet. Initially the sheet is laid on the length of the die at the startof pressing, and the punch executes a curvilinear motion on plunginginto the die.

Also the problem is solved in the case of an apparatus of the kindstated at the outset, by a matching conical punch and die set withactuating means by which the punch is insertable along a curved pathinto the die.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in detail, by way ofexample, with reference to the drawings, in which

FIG. 1 is a schematic side view of a press apparatus with punch and die;

FIGS. 2a, 2 b show cross-sections through punch and die;

FIG. 3 shows the apparatus of FIG. 1 at the start of the pressingoperation;

FIG. 4 shows the apparatus of FIG. 1 during the pressing operation;

FIG. 5 shows the apparatus of FIG. 1 at the end of the pressingoperation; and

FIG. 6 shows additional forming wings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a highly schematic side view of an apparatus for taper formingmetal sheets. Shown in the figure is a die 1 which has an internalcavity 2 tapering in the longitudinal direction as indicated in thefigure by the broken line 3 representing the lowest surface line of theconical cavity 2, which forms part of a truncated cone. FIGS. 2a and 2 bshow the die 1 with its conical cavity 2 in vertical section along thesection lines B—B and C—C of FIG. 1. The punch 4 is likewise formed witha conical taper in the longitudinal direction as part 12 of a truncatedcone, and, in the region intended to plunge into the die 1, matches theshape of the conical cavity, less the thickness of the sheet to beformed. The punch 4 is also shown in vertical section in FIGS. 2a and 2b , from which the conical shape of the punch part 12 is evident. In theregion that does not plunge into the die, the shape of the punch 4departs from that of the truncated cone (which is suggested by thebroken line 9), to facilitate removal of the tapered sheet. Instead ofthe round cross-sectional shape of punch and die shown in FIGS. 2a and 2b , any other desired conically tapering cross-sectional shapes could,of course, be used. In the example shown in FIG. 1, the punch 4 ispivotable about a pivot 5 so as to execute a curved movement asindicated by the arrow A as it plunges into the die 1. The drive for thepunch 4 may take the form of a crank arrangement 10, 11, which is shownonly schematically, and which moves the punch 4 into the die cavity 2where it presses on the sheet, and withdraws the punch 4 from the dieagain along the curved denoted by the arrow A. Suitable crank mechanismswill be familiar to the expert, and do not need further descriptionhere. Instead of a pivot 5 and a crank mechanism, any other desiredactuating elements can also be used, e.g. hydraulic or pneumaticactuating elements, which, as indicated in the following description,move the punch through the curve shown, or a curve of another form,into, and out of, the die.

FIG. 3 shows the same apparatus in a starting position, with a sheet 6to be formed overlying the die cavity. The punch 4 is arranged so thatin the starting position it contacts the sheet 6 substantially over itswhole length, so that the ensuing forming of the sheet commencessimultaneously over the entire length of the sheet. FIG. 4 shows thepunch 4 as it plunges with its curvilinear motion into the die 1, in aposition in which it has plunged about halfway into the die, which isshown transparently in the drawing so as to reveal the position of thepunch 4 within the die. FIG. 5 shows the punch 4 in its end position,the curved motion preferably being executed in such a way that the sheetis brought in contact with the bottom of the die substantiallysimultaneously over the whole length of the punch. In this way the sheetis tapered uniformly and made to conform to the shape of the punch anddie. In a known manner, bottoming may be performed in the end positionshown in FIG. 5 to prevent springback. Using the described technique forpressing the sheet in the conical die, a lateral region of the sheetblank can be shaped first, then in a further step, another lateralregion, and lastly, the central region, so that three pressingoperations are involved in the production of the taper tube shell. But alarger number of pressing strokes, e.g. five or seven strokes, may beperformed. The two marginal regions of the sheet blank may, however,have been preformed by other means, so that only the central part istapered in a single pressing stroke according to the invention. Asindicated schematically in FIG. 6, which shows a vertical sectionthrough a conical die and a conical punch, the central part of a sheetblank may for example also be tapered directly with punch and die, whilefor the marginal regions, forming wings 7 and 8 are additionallyprovided which are also conical, and can be closed around the punch 4 inthe direction of the arrows D by actuating elements (not shown) so thatthe marginal regions of the sheet are also pressed on to the die.

What is claimed is:
 1. A method for forming metal sheets into taper tubeshells, the metal sheets each having a length, the method comprising thesteps of: providing a conical die and matching conical punch cone havinga length; and pressing the metal sheet between the conical die andmatching conical punch cone at least one forming step, wherein theconical punch contact the metal sheet lying on the conical die at thestart of pressing substantially along the entire length of the metalsheet the conical punch executes a curvilinear motion on plunging intothe die, and the punch plunges into the die so as to arrive at thebottom of the die at the same instant substantially over the entirelength of the conical punch.
 2. Method according to claim 1characterized in that several forming steps are performed.
 3. Methodaccording to claim 1, characterized in that additional forming isperformed with forming wings above the die.
 4. Method according to claim1 characterized in that three or more forming steps are performed. 5.Method according to claim 1 characterized in that in the case of a sheetwith preformed marginal regions, a single forming step is performed inthe central region of the sheet.
 6. Apparatus for forming metal sheetsinto taper tube shells, comprising: a die with a conical forming cavity;a conical punch matched to the shape of the die; actuating means bymeans of which the punch is pivotable about a pivot and insertable alonga curved path into the die; and wherein the conical punch contacts themetal sheet lying on the die at the start of pressing, substantiallyalong the entire length of the metal sheet over the die and the punchplunges into the die so as to arrive at the bottom of the die at thesame instant substantially over the entire length of the conical punch.7. Apparatus according to claim 6, characterized in that additionalforming wings are provided by means of which sheet regions lying outsidethe die can be shaped.
 8. An apparatus for forming metal sheets intotaper tube shells, comprising: a die with a conical forming cavity; aconical punch having a length matched to the shape of the die; ahydraulic, or pneumatic, actuating means by which the lunch isinsertable along a curved path into the die; additional forming wingsare provided outside the die to shape regions of the metal sheet outsidethe die; and wherein the conical punch contacts the metal sheet having alength lying on the die at the start of pressing substantially along theentire length of the metal sheet over the die and the punch plunges intothe die so as to arrive at the bottom of the die at the same instantsubstantially over the entire length of the conical punch.